<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button>发送</button>
    <script>
        let x = null;
        const btns = document.querySelectorAll('button');
        let is = false;
        btns[0].onclick = function(){
            if(is){
                x.abort();
            }
            x = new XMLHttpRequest();
            is = true;
            x.open('GET','http://127.0.0.1:8000/time');
            x.send();
            x.onreadystatechange = function(){
                if(x.readyState === 4){
                    is = false;
                }
            }
        }
        btns[1].onclick = function(){
            x.abort();
        }
    </script>
</body>
</html>